Two-Dimensional First-Order Phase Separation in an Epitaxial Layer
Studying adsorbate ordering at the submonolayer level on clean surfaces is a crucial step in understanding the structure of epitaxial films during the initial stages of growth. An adsorbed atom interacts with other adsorbed atoms as well as with the substrate. The interactions are called adsorbated-adsorbate (A-A) and adsorbated-substrate (A-S) interactions, respectively. A simple nearest neighbor A-A attractive interaction can lead to the condensation of two-dimensional (2-D) overlayer islands with an (1 × 1) structure . Many epitaxial systems (especially in the case of homoepitaxy) have this structure at appropriate substrate temperatures. In the electron diffraction techniques, all information on the (1×1) islands such as island shape and size distribution is contained in the angular distribution of the integral order beam intensity. Recent advancement in diffraction theory [2–5] allows one to extract the island size distribution from the integral order beam angular distribution of intensity. Two particularly interesting examples involving high-resolution low-energy electron diffraction study of submonolayer ordering are Si homoepitaxy by Grownwald and Henzler , and W homoepitaxy by Hahn, Clabes and Henzler . Depending on the annealing temperature, a distribution of (1 x 1) islands were formed at a submonolayer coverage.
KeywordsFree Energy Density Free Energy Barrier Regular Solution Model Electron Diffraction Technique Submonolayer Coverage
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